L5- The Cardiovascular System V (Micro-anatomy of the Heart and Blood Vessels)

What are the three main types of blood vessels?

• Arteries: Carry blood away from the heart (oxygenated except for pulmonary and umbilical arteries).

• Veins: Carry blood toward the heart (deoxygenated except for pulmonary and umbilical veins).

• Capillaries: Facilitate exchange of gases, nutrients, and waste with tissues.

What are the three layers of blood vessel walls?

• Tunica interna (intima): Single layer of endothelial cells, wavy in arteries, smooth in veins.

• Tunica media: Smooth muscle layer, thicker in arteries, responsible for vasoconstriction/dilation.

• Tunica externa (adventitia): Connective tissue for support, thicker in veins, contains vasa vasorum.

What is the difference between arteries and veins?

• Arteries: Thick tunica media, high-pressure system, elastic fibers for recoil.

• Veins: Thinner walls, larger lumens, low-pressure system, contain valves to prevent backflow.

What are the three types of arteries?

• Elastic (conducting) arteries: Thick-walled, near the heart (e.g., aorta), highly elastic.

• Muscular (distributing) arteries: Deliver blood to organs, active in vasoconstriction (e.g., renal artery).

• Arterioles: Smallest arteries, regulate blood flow into capillaries.

What are the types of veins?

• Venules: Smallest veins, no valves.

• Medium veins: Thin walls, some valves to prevent backflow.

• Large veins: Thick tunica externa, carry blood back to the heart (e.g., vena cava).

What are the three types of capillaries and their characteristics?

• Continuous capillaries: Least permeable, tight junctions, found in muscles, lungs, brain.

• Fenestrated capillaries: Have pores, allow nutrient exchange, found in intestines, kidneys.

• Sinusoidal capillaries: Most permeable, large gaps, found in liver, spleen, bone marrow.

What are the three layers of the heart wall?

• Epicardium: Outer layer, contains blood vessels and nerves.

• Myocardium: Thick muscle layer responsible for contraction.

• Endocardium: Inner layer, lines heart chambers.

What is the function of Purkinje fibers?

Specialized cardiac muscle fibers help conduct electrical impulses to coordinate heart contraction.

What are intercalated discs?

• Structures between cardiac muscle cells containing gap junctions (electrical connection) and desmosomes (mechanical strength).

How does cardiac muscle differ from skeletal muscle?

• Self-excitable (SA node initiates contractions).

• Cells contract as a unit (gap junctions synchronize activity).

• Longer refractory period (prevents tetany).

What is the main energy source for cardiac muscle?

• Aerobic metabolism (oxygen-dependent).

• Contains many mitochondria for ATP production.

What are the key steps in the mechanism of cardiac contraction?

• Resting membrane potential (-90 mV).

• Depolarization: Sodium (Na⁺) influx, cell becomes positive inside.

• Plateau phase: Calcium (Ca²⁺) influx balances potassium (K⁺) efflux.

• Repolarization: K⁺ efflux restores resting potential

Why does the heart have a plateau phase?

Prevents premature contractions (sustains contraction for effective blood ejection).

Clinical Scenario: What happened in the clinical case of Jane (irregular heart rate)?

• Excessive caffeine consumption caused increased sympathetic stimulation, leading to tachycardia (rapid heart rate).

Clinical Scenario: Why did the clinician recommend deep breathing?

• Activates the parasympathetic nervous system (vagus nerve).

• Lowers heart rate and stabilizes rhythm.

What is the vasa vasorum?

• Small blood vessels in the tunica externa that supply large arteries and veins.

How do elastic arteries function in circulation?

• Expand during systole (ventricular contraction) and recoil during diastole to maintain blood pressure.

What is active vasoconstriction and where does it occur?

• Constriction of blood vessels to regulate flow.

• Happens in muscular arteries and arterioles.

Where does the slowest blood flow occur and why?

• Sinusoidal capillaries (e.g., liver, spleen, bone marrow).

• Slow flow allows for large molecule exchange (proteins, cells).

Which capillary type is best for nutrient absorption?

• Fenestrated capillaries (small intestine, kidneys).

Which areas of the body lack capillaries?

• Cartilage, epithelium, tendons, ligaments.

• Receive nutrients via diffusion from nearby vessels.

How do veins ensure blood returns to the heart?

• Valves prevent backflow.

• Skeletal muscle contraction assists venous return.

• Respiratory pump (breathing) helps move blood.

Why are veins considered blood reservoirs?

• Hold ~60% of total blood volume due to their large lumen and low-pressure system.

What is the primary function of arterioles?

• Regulate blood flow into capillary beds.

• Major site of resistance in circulation (vasoconstriction/dilation controls blood pressure).

How does the structure of blood vessels relate to function?

• Arteries: Thick walls, high pressure, elasticity for expansion and recoil.

• Veins: Thin walls, large lumens, valves for low-pressure blood return.

• Capillaries: Thin-walled for efficient exchange.